1. Field of the Invention
The present invention relates to a process for producing a sandwich molded article whose skin (outer layer) is not uniform in thickness in parts.
In particular, the present invention relates to a mud guard for automobile and a molding attached to each side of an automobile, its bumper, etc., and a process for producing them.
2. Description of the Related Art
As a process for sandwich molding of a synthetic resin, there is, for example, the technique disclosed in Japanese Patent Application Kokoku No. 52-11336. The technique disclosed in the above reference comprises injecting a non-multicellular material for skin into the cavity of a mold through an injection nozzle at first, further injecting thereto a material for inner core which is made multicellular by a blowing agent, and thereby producing a synthetic resin sandwich molded article composed of the non-multicellular skin material and the inner-core material which has been made multicellular. When this technique is utilized, there can be produced a sandwich molded article composed of a hard core layer in the inner part and a soft skin coated thereon.
In a certain molded article, there is a portion which is desired to be composed of a sandwich molded article wherein a part of its skin is thick and the other part thereof is thin. That is, flexibility is imparted to a part of the sandwich molded article by thickening the skin, and stiffness is imparted to the other part by thickening the core layer by thinning the skin.
For example, as shown in FIG. 8 and FIG. 9, the mud guard 4 for automobile disclosed in Japanese Patent Application Kokai No. 1-233178 comprises a main body 41 and a mounting part 43 which are to be attached to a car body, and a lower piece 42 suspended under them.
The main body 41 has mounting holes 411 and 412 for inserting bolts. The mounting part 43 has the same mounting hole 431 as them. Between the main body 41 and the mounting part 43, a hollow 45 surrounded by them is provided. The hollow 45 is a portion into which a part of a car body is to be inserted. As shown in FIG. 9, the section structure of the mud guard 4 is such that a core layer material 3 is enveloped in parts in a skin material 2 by reducing the thickness of the lower piece 42. A flexible synthetic resin is used as the skin material 2. On the other hand, a rigid synthetic resin is used as the core layer material 3. In short, the mud guard consisting of said sandwich molded article has flexibility and stiffness imparted by enveloping the rigid core layer material 3 in the flexible skin material 2 in parts.
In the above-mentioned mud guard, the main body 41 and the mounting part 43 are required to have a high stiffness because they are attached to a car body by using the mounting holes 411, 412 and 431. On the other hand, the lower piece 42 is required to have flexibility which is such that the lower piece 42 undergoes elastic deformation easily when brought into contact with, for example, a block for division in a parking zone. However, in conventional processes for producing a sandwich molded article, the design of the molded article is limited because the molded article is obtained by varying its thickness, as described above. These processes are disadvantageous also in that owing to the influence of the core layer, no satisfactory decorative surface can be obtained in a portion in which the skin is thin.
On the other hand, as a side molding attached to each side of an automobile, there has been known a side molding comprising a main body of molding made of rubber or synthetic resin and a metal strip extending in the longitudinal direction of the main body which is embedded in the main body [Japanese Utility Model Registration Kokai No. 54-1809]. The metal strip embedded in the main body of molding has an adhesive previously applied thereon for adhering the metal strip to the main body of molding. The metal strip suppresses warping of the side molding and prevents peeling of the side molding from the body of an automobile.
As another side molding, there is known a side molding comprising a main body of molding (a basal part) made of a flexible resin such as a polypropylene blend with an ethylene-propylene-diene terpolymer rubber (hereinafter referred to as EPDM), and a core therein made of a rigid resin such as a polypropylene containing talc, said rigid resin having a coefficient of linear expansion smaller than that of said flexible resin [Japanese Patent Application Kokai No. 2-200543]. By virtue of such a constitution, the side molding has stiffness and softness of the surface and is prevented from changing in size.
However, in the case of the former side molding, common rubber or resin used as a material for the surface portion of the main body of molding does not have sufficient adhesive properties, and hence a primer is needed when a coating layer is formed on the surface of the side molding. Moreover, the former side molding has been disadvantageous in that an adhesive should be previously applied on the metal strip in order to improve the adhesion of the metal strip to the main body of molding.
The latter side molding has been disadvantageous in that the polypropylene blend with EPDM which constitutes the main body of molding does not have sufficient adhesive properties, and that the adhesion between the main body of molding and the core is low.